GPS Jamming

We’ve discussed the military’s overdependence on GPS guidance (see, "GPS - The Navy's Addiction") and briefly noted the adverse effects if the GPS signal could be jammed.  US guided weapons are heavily dependent on GPS as their primary guidance mode.  While other modes are available, they are far less accurate.  This is disturbing because accuracy, or precision guidance, was the cornerstone of the Second Offset Strategy, and the loss of that capability would be devastating.  We’ve justified our reduced numbers of ships and aircraft in large measure by the claim that our weapons are so much more accurate than they were that we no longer need as many.  This is foolish to the nth degree but is, nevertheless, the basis of the rationale for reduced numbers.  If our weapons could be rendered significantly less accurate and we have lesser numbers compared to our enemies, we would be in serious military trouble!

Can a GPS signal be jammed?  Apparently, it’s quite easy.  GPS signals operate at very low power and over a very narrow frequency range – the ideal combination for jamming or disruption.

“GPS signals, transmitted at low power from distant satellites, are uniquely susceptible to jamming.” (1)

“A 1-kilowatt jammer can block a military GPS receiver from as far away as 80 kilometers (50 miles). A Russian company recently marketed a 4-[kilo]watt jammer that can deny a standard GPS signal within up to 200 kilometers (125 miles).” (1)

North Korea has reportedly jammed GPS signals over South Korea on over 100 occasions.  The jamming reportedly affected aircraft, ships, cell phones, and cars.

“North Korea reportedly purchased truck-mounted GPS jammers from Russia with a range of thirty to sixty miles, and in 2011 was reportedly at work on even longer-range jammers.” (2)

Some weapons offer alternative navigation modes such as Terrain Contour Matching (TERCOM), Digital Scene Matching Area Correlation (DSMAC), and Inertial Navigation (INS), however, these have significant drawbacks and limitations.  Two of those options require the weapon route to have been pre-mapped which is not always possible.  INS is inherently inaccurate.

Supposedly, military GPS signals are more resistant to jamming and disruption but I’ve been unable to find any authoritative information on that.

As we ponder GPS issues, here is an example from personal experience.  Not too long ago, I had the pleasure and privilege of touring a Cyclone class PC that was docked at a large US city.  I noticed that the ship’s GPS navigation system showed the vessel to be about 30 miles inland, in the middle of a park.  Screwed into the bulkhead next to the ship’s system was a commercial GPS navigation display from a well known outdoor camping gear store.  I asked the crew about it and was told that they had used their own money to purchase the commercial unit because the ship’s system was never right.  They simply used the commercial unit which was always dead on.

I don’t know how widespread accuracy and reliability issues are with military GPS units but I’ve got to believe this was not an isolated incident.  If we have significant numbers of ships using commercial units then we’ve made ourselves extremely vulnerable to GPS jamming and disruption.  This also suggests that we need to relearn how to navigate without GPS.

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(1)MIT Technology Review website, “How Cruise Missiles Would Beat GPS Jammers in Libya”, Christopher Mims, 20-Mar-2011,

https://www.technologyreview.com/s/423363/how-cruise-missiles-would-beat-gps-jammers-in-libya/

(2)Popular Mechanics website, “North Korea Is Jamming GPS Signals”,  Kyle Mizokami, Apr 5, 2016,

http://www.popularmechanics.com/military/weapons/a20289/north-korea-jamming-gps-signals/

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